Seasonal effects on bipolar disorder: A closer look

https://doi.org/10.1016/j.neubiorev.2020.05.017Get rights and content

Highlights

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    A comprehensive review of circadian disturbances in bipolar disorder is provided.

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    Individuals with bipolar disorder also exhibit seasonal patterns of illness onset.

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    We examine the monthly rate of change of solar insolation at 51 sites globally.

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    Sites at the same latitude can display markedly different solar insolation.

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    Local solar insolation trends may inform predictive management of bipolar symptoms.

Abstract

Bipolar disorders have an onset in late adolescence or early adulthood and patients may experience alternating episodes of mania and depression, with euthymic periods interspersed between these extremes of mood. Clinical research studies have shown that bipolar disorder patients exhibit disruptions in circadian and seasonal rhythms, even when they are symptom free. In addition, some bipolar patients display pronounced seasonal patterns in occurrence of manic and depressive episodes, time of year for disease onset, and age of onset. Several groups have emphasized the impact of seasonal changes in sunlight intensity on bipolar disorder, especially in locations farther from the equator. In this paper, we examine rate of change of solar insolation during the spring and fall in locations that vary in their distance from the equator and propose that seasonal changes in sunlight intensity may be tracked by the suprachiasmatic nucleus and affect disease onset and progression in seasonally susceptible bipolar patients.

Section snippets

Components of circadian time keeping

Experiments with a variety of mammalian species over the past 50 years have confirmed that the suprachiasmatic nuclei (SCN), located at the base of the anterior hypothalamus just above and on either side of the optic chiasm and in close proximity to the third ventricle, represent the key circadian pacemakers in the brain. Each nucleus is composed of approximately 10,500 neurons in laboratory rats, with an endogenous period of approximately 24 h that is constantly synchronized by external

Properties of circadian rhythms in humans

Clinical research has confirmed that many properties of circadian rhythms first described in laboratory animals also apply to humans. Importantly, human behavioral and endocrine rhythms persist under constant environmental conditions (e.g. constant dim light), with phase-setting of rhythms by environmental light such that internal pacemaker activity resets to match with the newly occurring external light-dark cycle. In addition, human circadian rhythms vary based upon seasonal changes in day

Overview of bipolar disorder

Bipolar disorder (BD) is a severe mental disorder that affects approximately 1–4 % of the population worldwide, is a significant cause of disability, and includes a high rate of suicide attempts and suicide completions. Individuals with bipolar I disorder exhibit at least one episode of mania, while those with bipolar II disorder display at least one hypomanic episode and one depressive episode. Hypomania is less intense than mania, but both conditions involve some level of circadian

An evolutionary view of bipolar disorder

It is not unreasonable to ask why BD, which has a very high heritability, has been maintained at a stable rate in most ethnic groups when it appears on the surface to be so deleterious. Modern humans (Homo sapiens) originated in Africa in close proximity to the equator. This place of origin provided an environment with a relatively unchanging photoperiod of approximately equal amounts of daylight and darkness each day throughout each year. As early humans started to migrate north into areas of

Early studies of circadian disturbances in BD

Given the inherent cyclicity of manic and depressive episodes that characterize BD, it is not surprising that clinicians have for many years examined connections between BD and disturbances in circadian rhythms (Table 2). Some of the earliest clinical reports of circadian disturbances in patients with mental disorders were summarized by a basic scientist with interests in biological rhythms in laboratory animals and humans. Dr. Curt P. Richter of the Phipps Clinic at The Johns Hopkins Hospital

Genome-wide association studies

The heritability of BD has been estimated to be 85 % based upon a study of 67 monozygotic and dizygotic twin pairs, with little or no evidence of a contribution from the familial environment (McGuffin et al., 2003). The first large-scale collaborative genome-wide association study (GWAS) of BD involved a comparison of 7481 BD patients with 9250 unaffected controls (Sklar et al., 2011). This initial report from the Psychiatric Genomics Consortium (PGC) combined with other GWAS identified a total

Seasonal patterns of BD

As was mentioned earlier in this paper, many animal species, including humans, appear to be capable of detecting seasonal changes in photoperiod as well as to meteorological variables such as ambient temperature and atmospheric pressure (DiNicola et al., 2020). In their treatise on manic depressive illness, Goodwin and Jamison (2007) noted that seasonality affects the timing of manic and depressive episodes and also has a profound effect on suicide attempts. They also combed through archives

A new approach to seasonal effects on BD

Daylength (photoperiod) is at a minimum at the winter solstice and at a maximum at the summer solstice. Because the orbit of the earth around the sun is elliptical, the rate of change in photoperiod in the northern and summer hemispheres increases heading into and exiting the solstices. Photoperiod increases from the winter solstice to the summer solstice, but astronomically the rate at which photoperiod increases peaks at the spring equinox. Likewise, the rate at which photoperiod decreases

Summary

Circadian and seasonal rhythms in humans share many characteristics with those of laboratory animals that have been studied under highly controlled environmental conditions. Although humans have been capable of artificially controlling ambient levels of light after sunset for the past several centuries, most of the evolutionary history of humans has involved detection as well as anticipation of daily and seasonal changes in photoperiod.

BD by its very nature represents a cyclic pattern of

Implications

The formal announcement of the precision medicine initiative in the United States (Collins and Varmus, 2015) represented a major turning point in approaches to diagnosis and treatment of diseases, especially cancers. A major goal of this initiative is to employ molecular and phenotypic markers to improve the accuracy of diagnosis and the selection of treatments that will result in improved patient outcomes across many medical specialties. A major question for the field of psychiatry is to what

Funding

The preparation of this review article did not benefit from any grant support from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Competing Interest

The authors declare no conflicts of interest in the preparation of this review article. They collaborated in reviewing the relevant literature, analyzing the solar insolation data and writing the article and are responsible for its content.

Acknowledgements

Travis Josephs received support from the Vanderbilt University Undergraduate Immersion Program.

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